The great advantage of the circuit shown in the figure is that its frequency is controlled by a direct voltage. This allows the circuit to be used in conjunction with digital to analog converters (DAC) by controlling the frequency through either a PC parallel output or a microprocessor. The varicap may be of the double type as shown in the diagram or, in the absence thereof, two separate variacaps such as BB809 may be used which are relatively common in our market. diameter causes the circuit to generate centralized signals at approximately 3.5 MHz. The capacitors used in the circuit must be ceramic and the junction field effect transistor (JFET) admits equivalents such as the MPF102. The circuit can generate signals of up to a few dozen megahertz by simply changing the coil to the desired range. The width of the swept range basically depends on the characteristics of the varicap used.
